The present invention relates to a powered screening apparatus, and more particularly, to a variable frequency screening apparatus used to separate and sort multiple size solids and particulates.
Vibrating screen arrangements have been used for many years in gravel and rock quarrying for sizing rock product and/or for removing undesirable material from the eventual finished product. Generally, the arrangements comprise a working member supported on a frame and an exciter arranged to impart vibrating motion to the member. The working member is fitted with a screen deck with a conventionally rigid aperture element which may be made up of a plurality of screening panels.
Despite the fact that the working member is vibrated in use, blinding of the apertures in the screening material occurs. When blinding occurs, separation of particulates becomes less uniform and less efficient. It is, therefore, an object of this invention to reduce blinding and improve efficiency.
Vibrating screen decks have been used widely in the past for separating particulates of various sizes and composition. Such screening decks typically comprise a rectangular frame suspended in operation with screen cloth mounted within the frame from which the materials are separated. The frame and screen in such decks are suspended at an angle. The entire frame is vibrated, thus imparting vibration to the machine which in turn causes the solids to move down the screen. As materials move down the vibrating screen, the solids of smaller mesh size pass through the screen with larger solids discharged from the lower end of the screen.
One disadvantage of such prior screening devices is imparting vibration to the entire system without a corresponding reduction in the blinding. Decks of this size can typically employ motors of forty horsepower (40 h.p.) or more. Another disadvantage of such prior decks is the susceptibility of frequent maintenance because the vibration is imparted to the entire deck for sustained lengths of time thus causing stress on joints of various fitted parts. Accordingly, it is an object of this invention to reduce stress on the joints of the various fitted parts.
Other screening apparatus have been developed which attempt to reduce a substantial energy requirement in such devices. In these apparatus, a plurality of small vibrator motors have been employed which are coupled to tappet shafts extending beneath the screen material at various locations spaced along the length of the screen. The tappet shafts are coupled by relatively complex linkages to a vibrator motor on the exterior of the frame deck. A plurality of tappet shafts or arms are positioned on the shaft which move eccentrically to strike the screen from beneath. The particular tappet arrangements in such decks necessitate relatively complex linkages and cause localized tapping of the screen both of which result in concentrated wear. Such power screening decks require frequent adjustment to keep the screen in contact with the tappets. Such prior screening decks are also susceptible to frequent blinding. It is, therefore, an object of this invention to eliminate the complex linkages, reduce frequent necessity for adjustment and increase the efficiency of the screening deck.
Yet another disadvantage of such prior screening devices is the inability to independently adjust the frequency with which various tappets spaced beneath the screen strike the screen. With other devices, the frequency with which tappets strike the screen is uniform. This uniform frequency causes a constant motion to the screening surface which in turn exacerbates blinding. It is, therefore, an object of this invention to permit the relative frequency that the tappets strike the screen to be selectively adjusted to vary the screen vibration which in turn reduces blinding and improves screening efficiency.